Many electronic devices are subjected to burn-in and/or test procedures at some point during or after the fabrication process. For burn-in and test, the packages containing the electronic device must be removeably mounted on or in a test fixture or socket which provides electrical connection with each of the package input/output terminals while the device is functionally tested and evaluated. In many cases the device package is subjected to harsh environmental conditions (such as heat, etc.) as well as electrical stresses to evaluate and assure full functionality of the finished device. In order to provide effective testing and burn-in, the fixture in which the device package is mounted for testing and burn-in must permit rapid and easy insertion and removal without damage to the electronic device, the device package or the device package input/output terminals. The socket must also withstand repeated use without failure or diminished reliability.
A variety of zero insertion force test sockets have evolved in response to this need. Most are designed so that a device package may be mounted using vacuum pencils and the like as employed in automated pick and place systems. Electrical contact fingers within the various sockets provide electrical connections with the device package terminals and grip the terminals to retain the device packages within the socket. Since the contact fingers physically retain the device package, means must be provided for opening and closing the contact fingers to facilitate insertion and removal of the device package. Since an opening and closing cycle must occur for each package tested, automation of these steps is highly desireable.
Typical device package test sockets, such as disclosed in U.S. Pat. No. 4,491,377, respond to a vertical force which activates a spreader to spread the ends of electrical contact fingers within the socket. When the ends of the contact fingers are spread, the device package is inserted into the socket through a top opening. After the device package is in place, the vertical force is removed and the spreader retreats, allowing the contact fingers to close against and grip the terminals on the device package. Since the device packages are inserted from the top, insertion may be performed by gravity and/or with automated pick and place systems. Since the pick and place machinery basically moves in the vertical direction, it is a simple matter to apply a vertical force to the spreader to open and close the contact fingers. This arrangement, however, is not well adapted to mounting device packages utilizing ball grid array, pin grid array or other terminal configurations which require the contact fingers to all move simultaneously in the same direction toward and away from the device package terminals transversely to the direction of loading and unloading.
Sockets as disclosed in U.S. Pat. No. 4,950,980 are intended to accommodate device packages with downwardly projecting leads or terminals. The device package rests on a moveable cam plate. After the device package is inserted into the socket, the plate is activated (via cam means) to move in a lateral direction. The lateral movement repositions the device package so that its leads or terminals are brought into contact with the contact fingers of the socket. The cam is operated by a lever which moves laterally. By moving only in the lateral direction, however, the lever may not be automated using the vertical movement of the pick and place equipment used to deposit the device packages in the sockets.
Another socket which utilizes a laterally moving cam plate is disclosed in application for United States Letters Patent entitled Mounting Apparatus for Ball Grid Array Device filed Jun. 10, 1994, under Ser. No. 08/258,348. This socket is designed to accommodate a device package with ball grid array terminals projecting downwardly into apertures in a support plate. While the device package is held stationary, a cam activates an underlying cam plate which moves the contact fingers toward the terminals of the ball grid array. The cam is operated by a lever which is not amenable to activation by the vertical movement of conventional automated operations using pick and place equipment.